The present invention is directed to ink compositions and to processes for the preparation and use thereof. More specifically, the present invention is directed to compositions suitable for use in ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises (a) water; (b) Acid Yellow 23 dye; and (c) urea.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or noble. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 4,840,674 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses an improved ink composition which comprises a major amount of water; an organic solvent selected from the group consisting of tetramethylene sulfone; 1,1,3,3-tetramethyl urea; 3-methyl sulfolane; and 1,3-dimethyl-2-imidazolidone; which solvent has permanently dissolve dissolved therein spirit soluble dyes such as black, yellow, cyan, magenta, brown, and mixtures thereof.
U.S. Pat. No. 5,006,170 (Schwarz et al.) and U.S. Pat. No. 5,122,187 (Schwarz et al.), the disclosures of each of which are totally incorporated herein by reference, disclose hot melt ink compositions suitable for ink jet printing which comprise a colorant, a binder, and a propellant selected from the group consisting of hydrazine; cyclic amines; ureas; carboxylic acids; sulfonic acids; aldehydes; ketones; hydrocarbons; esters; phenols; amides; imides; halocarbons; urethanes; ethers; sulfones; sulfamides; sulfonamindes; phosphites; phosphonates; phosphates; alkyl sulfines; alkyl acetates; and sulfur dioxide. Also disclosed are hot melt ink compositions suitable for ink jet printing which comprise a colorant, a propellant, and a binder selected from the group consisting of rosin esters; polyamides; dimer acid amides; fatty acid amides; epoxy resins; fluid paraffin waxes; fluid microcrystalline waxes; Fischer-Tropsch waxes; polyvinyl alcohol resins; polyols; cellulose esters; cellulose ethers; polyvinyl pyridine resins; fatty acids; fatty acid esters; poly sulfonamides; benzoate esters; long chain alcohols; phthalate plasticizers; citrate plasticizers; maleate plasticizers; sulfones; polyvinyl pyrrolidinone copolymers; polyvinyl pyrrolidone/polyvinyl acetate copolymers; novalac resins; natural product waxes; mixtures of linear primary alcohols and linear long chain amides; and mixtures of linear primary alcohols and fatty acid amides. In one embodiment, the binder comprises a liquid crystalline material.
Acid Yellow 23 dye has several color advantages over other yellow dyes used in ink compositions. Acid Yellow 23 dye also, however, can be difficult to dissolve in many common ink vehicles. Use of Acid Yellow 23 dye in ink vehicles commonly used for thermal ink jet printing can result in problems such as high particle counts in freshly made inks and increasing particle counts in the inks over time, which in turn can lead to clogging of jets in the printer or other particle-related failure modes as the inks age. In addition, inks containing Acid Yellow 23 dye can exhibit ink crusting on the printhead's front face and elsewhere upon drying or when heated. Acid Yellow 23 containing inks often have very low measured first drop latency, low recoverability, and low functional latency, and excessive orange crusting is often observed on the front face of the printhead. In addition, Acid Yellow 23 containing inks can exhibit instability after freeze/thaw cycling, with the dye precipitating from the ink after a single freeze/thaw cycle. These disadvantages of Acid Yellow 23 dye can sometimes be addressed by lowering the relative amount of the dye in the ink, but the resulting ink then may exhibit inferior color gamut and/or optical density.
Accordingly, while known compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions suitable for use in ink jet printing processes. In addition, a need remains for ink compositions with desirable yellow color characteristics. Further, a need remains for ink compositions with desirable yellow color characteristics which exhibit reduced crusting when used in an ink jet printer. Additionally, a need remains for ink compositions with desirable yellow color characteristics which exhibit improved recoverability, improved maintainability, and improved functional latency when used in an ink jet printer. There is also a need for ink compositions with desirable yellow color characteristics which exhibit reduced particulates in the ink. In addition, there is a need for ink compositions with desirable yellow color characteristics which exhibit low intercolor bleed when printed next to inks of other colors. Further, there is a need for ink compositions with desirable yellow color characteristics which exhibit improved freeze/thaw stability. Additionally, there is a need for ink compositions containing Acid Yellow 23 dye wherein the dye is present in the ink in desirably high concentrations.